The functional vessels of human and animal bodies, such as blood vessels and ducts, occasionally weaken or even rupture. For example, in the aortic artery, the vascular wall can weaken or tear, resulting in dangerous conditions such as aneurysms and dissections. Upon further exposure to hemodynamic forces, such an aneurysm can rupture.
One treatment for aneurysms includes the use of a stent grafts that are placed within the vascular networks and that include one or plural stents affixed to a graft material. The stent grafts are secured at the treatment site by endovascular insertion utilizing inducers and catheters, whereafter they are enlarged radially and remain in place by attachment to the vessel wall. In particular, stent grafts are known for use in treating descending thoracic and abdominal aortal aneurysms where the stent graft at one end defines a single lumen for placement within the aorta and the other end is bifurcated to define two lumens, for extending into the branch arteries. It is important that stent grafts can effectively exclude the aneurysm by sealing both proximally and distally to the aneurysm, such that the patient's blood flow is shunted through the stent graft. A device of this type can, for example, treat various arterial aneurysms, including those in the thoracic aorta, abdominal aorta, iliac, or hypogastric artery.
One example of such a stent graft is disclosed in PCT Publication No. WO 98/53761, in which the stent graft includes a sleeve or tube of biocompatible graft material such as Dacron™ polyester fabric (trademark of E.I. DuPont de Nemours and Co.) or polytetrafluoroethylene defining lumen, and further includes several stents secured therealong, with the stent graft spanning the aneurysm extending along the aorta proximally from the two iliac arteries; the reference also discloses the manner of deploying the stent graft in the patient utilizing an introducer assembly.
Another known stent graft is the Zenith AAA™ stent graft sold by Cook Group Incorporated, Bloomington, Ind.
Stent grafts may be susceptible to certain latent complications, such as instability leading to kinking, obstruction of the lumen and/or disintegration leading to possible graft explantation. The stent graft may undesirably move out of its intended position mostly due to larger displacement forces within the smaller diameter stent graft portions.
Stent grafts may also be susceptible to different types of endoleaks. In some cases, endoleaks allow relapse of the conditions the stent grafts are employed to treat. Endoleaks are sometimes caused or aggrevated by graft migration, in addition to other factors.
Therefore, two closely related aspects of stent graft function are sealing and fixation. Often, a stent graft engages the wall of the lumen on both ends of the aneurysm or other defect, at proximal and distal regions referred to as landing or sealing zones. Typically these sealing zones are located near the termini of the stent grafts. The seal between the stent graft and the vascular wall is typically formed at these locations as a result of the circumferential apposition of the stent graft to the vascular wall, where this apposition is typically maintained by the radial force of the stents that are attached to the stent graft.
It is also desirable to fix, or anchor, the stent graft in place. For some abdominal aortic aneurysm stent grafts, proximal fixation in the neck region of the aorta is critical for long term durability of endoluminal repair.
To date, fixation or anchoring of the stent graft has been achieved using a variety of anchoring mechanisms. For example, one known anchoring mechanism relied on the frictional forces that exist between the stent graft and aortic wall due to the radial force supplied by the stent. Another method of anchoring the stent graft involved tissue incapsulation, wherein exposed stent struts and other parts of the stent graft may eventually become completely encapsulated by tissue growth, thereby assisting fixation.
Fixation was also achieved by fixation at the top or proximal end by barbs or small hooks or by a stent portion that is uncovered by graft material and could be incorporated into the vessel wall. Distal end fixation was attained by friction within the branch or iliac arteries.
In another example of a prior art stent graft described in U.S. Pat. Pub. No. 2001/0037142 A1, graft fixation was achieved by keeping the proximal end of the main stent graft body unattached to the vessel wall and including an attachment tube including an attachment stent for vessel wall attachment at the aneurysm proximal neck, with the attachment tube fully sealing the relative to the aorta while permitting free flow to the renal arteries.
It is therefore important to promote the formation of adequate seal and fixation, especially near the ends of stent graft.